The present invention relates to improved platelet enriched compositions for wound treatment and methods of making and use thereof.
There have been many different substances and methods developed in the past for treating wounds, depending upon the type and location and severity of the wound. A wound is generally defined as an injury to an area of the body of a human or animal. Although injury to the surface of the skin is the most well known type of wound, the surfaces of internal organs may also be wounded, such as during surgery, rupture of the spleen or liver, or resulting from traumatic blows to the body surface in the vicinity of an internal organ.
Medical practice characterizes wounds as chronic or acute, according to the persistence and severity of the wound. A chronic wound is one that is prolonged or lingering, rather than promptly healed. An acute wound is one that occurs relatively quickly, and heals relatively quickly as well. Tissue wounds may have a wide spectrum of manifestations, as small as merely an abnormal microscopic tear or fissure in tissue (or a surface thereof), or as large as the abrasion or ablation of the skin covering a substantial portion of the body, such as in a burn victim. Acute wounds covering a large or movable surface are usually the most difficult to guard from infection, and to heal.
Blood and bodily fluids include various substances that affect wound healing. The blood is the primary medium for delivering healing agents to the wound site, and for transporting foreign or harmful substances away from the wound. Whole blood is primarily comprised of three main types of cells suspended in a protein rich solution known as plasma. The three main cell types in whole blood are erythrocytes (a.k.a. red blood cells), leukocytes (a.k.a. white blood cells) and thrombocytes (a.k.a. platelets). The red blood cells are the iron-containing cells that facilitate the transport and transfer of oxygen to body tissue, and the removal of carbon dioxide. The white blood cells perform a variety of functions such as phagocytosis of foreign bodies and production of antibodies, and are primarily responsible for fighting infection and foreign substances within the blood or wound site. Platelets perform many functions such as plugging leaks in blood vessels and helping begin the process leading to the formation of a blood clot; platelets contain substances known as growth factors that facilitate the formation of new tissue.
Although there are several methods for separating whole blood into its various components, one of the most convenient and expeditious methods is accomplished by differentially centrifuging blood or some of its components (i.e., apheresis). Using apheresis, the red and white blood cells and plasma may be separated out and returned to the donor""s or patient""s body, leaving the sequestered platelets in essentially concentrated form for use in wound healing techniques. From blood extracted from a patient, the platelets may thus be obtained and activated for use on the same patient; methods of using a patient""s own blood are called xe2x80x9cautologousxe2x80x9d or xe2x80x9cautogenicxe2x80x9d donor methods. Methods using blood donated by one or more third parties for use by a patient are called xe2x80x9chomologousxe2x80x9d or xe2x80x9cheterologousxe2x80x9d donor methods, or collectively called xe2x80x9callogenicxe2x80x9d methods.
One of the proteins suspended in plasma is fibrinogen, which reacts with substances released into (or attracted by) wound sites to produce sticky strands of fibrin. Such reactions result in the cross linking of the fibrin strands to form a mesh that holds and supports the deposit or growth of other tissue materials at the wound site.
The wound healing process is generally considered to occur in several stages, generally known as the healing cascade. After tissue injury, platelets are among the first cells to appear in the vicinity of the wound. Activation of a platelet by an agonist such as thrombin, or other agonists such as those listed elsewhere herein, leads to the release of granule material from within the platelet. Such granulation activation results in the release of proteins known as growth factors, primarily concentrated in the alpha granules of platelets. These released growth factors stimulate the formation of new tissue; when applied to wounds, growth factors have been known to increase the rate of collagen laydown, vascular ingrowth, fibroblast proliferation and overall healing. The release of a protein known as platelet-derived growth factor (PDGF) is a chemotactic signal for monocytes, neutrophils and fibroblasts which then move into the wound, to begin the inflammatory stage of the healing process. During this time, monocytes secrete a number of factors including PDGF and transforming growth factor-xcex21 (also found in platelets), which recruits and activates fibroblasts, to begin the repair stage of the healing process. Subsequently, wound healing continues through the process of collagen remodeling within the wound.
Based upon the foregoing general scientific principles, already known in the field are wound sealants made from biological materials obtained primarily from tissue other than blood platelets. An example is wound sealants such as xe2x80x9cfibrin gluexe2x80x9d, which often are essentially a mixture of co-coagulants (thrombin and calcium), concentrated fibrinogen and other coagulation proteins. In most applications, the primary roles of fibrin glue are to seal wound surfaces to prevent loss of blood and other body fluids after surgery, and to provide adhesion between adjacent tissue surfaces. These products form a hard, cast-like covering over the area to be sealed, and tend to be non-yielding to limb movement.
The production of fibrin glue often requires obtaining fibrinogen from blood through a process known as cryoprecipitation, including both freeze-thaw cycles and relatively lengthy centrifugation of plasma in controlled environments, to concentrate the fibrinogen in sufficiently for use; the precipitant thus obtained is frozen to xe2x88x9220xc2x0 to xe2x88x9230xc2x0 centigrade before storage. These requirements make such materials unsuitable for application during the course of surgery, especially emergency surgery without an hour or more lead time. Moreover, to the extent this process depends upon the use of autologous biological materials, using this process shortly before or during surgery may result in the loss of crucial bodily fluids during a time when the patient""s body is badly in need of such fluids. By contrast, substantially larger amounts of concentrated platelets can be more conveniently obtained within a matter of minutes from more recent methods of differential blood centrifugation not requiring freezing and without significant loss of bodily fluids.
While there has been much research concerning fibrin glue, this material belongs to a separate field from the present invention, primarily because fibrin glues typically contain cryoprecipitated proteins without platelets. The use of fibrin glue is discussed extensively in the scientific literature; for example, see the references cited in U.S. Pat. No. 5,585,007 issued to Antanavich et al on Dec. 17, 1996.
Wound treatment compositions derived from platelet enriched concentrates are known and possess certain advantages over materials without platelets such as fibrin glue. One reason is that natural wound healing agents are released by the platelets. Further, the concentration of platelets likewise allows for a concentrated amount of wound healing factors. Additionally, to the extent that the wound healing composition is made from the biological materials of the patient, the risks associated with heterologous donors (such as disease, immunologic reactions, or the like) are eliminated. Representative examples of platelet derived wound treatment compositions are described for instance in Hood U.S. Pat. No. 5,733,545; Knighton U.S. Pat. No. 5,165,938; and Gordiner U.S. Pat. No. 5,599,558.
Platelet concentrates are typically isolated by the process of differential centrifugation which essentially allows separating the patient""s own blood into at least three different components: packed erythrocytes (red blood cells), plasma and platelet concentrate. Platelet concentrate can be combined with a solution of either sodium or calcium mixed with thrombin (xe2x80x9ccalcified thrombinxe2x80x9d), which instantaneously form a composition of activated platelets that, when made with the necessary viscosity, can be utilized as a wound sealant. The chemical reactions and cascades that normally occur when thrombin is added to the concentrated platelets are indeed complex. See, for instance, Reeder, et al, in Proceedings of the American Academy of Cardiovascular Perfusion, Vol. 14, January 1993. Such wound sealants typically set up into a hard mass covering the application site, thereby sealing the site against further blood loss and external contaminants.
There are a number of disadvantages associated with conventional wound compositions derived from platelet concentrates. For instance, activation of platelets leads to instantaneous hardening of the material and thus requires the physician to both activate and apply the platelet composition to the wound site within seconds of activation. Also, certain platelet compositions must be applied to the wound site on a daily basis and thus require regular blood withdrawal from the patient. The presence of a hardened mass at the wound site is undesirable because it impedes oxygen transport into the wound which is necessary for tissue repair. It may also create a favorable environment for the growth of pathogenic anerobic bacteria.
Accordingly, an improved platelet enriched wound treatment composition which avoids or diminishes the problems associated with typical platelet enriched wound compositions would be desirable.
The present invention relates to an improved enriched platelet composition for wound treatment, a method of making and use thereof. The composition comprises platelets and an effective amount of an anti-oxidant, preferably ascorbic acid (vitamin C) so as to delay or prolong the activated gelation period to allow the practitioner sufficient time to apply the composition in liquid form to the wound site and to prevent the material from forming a hard seal. Optional antibiotics may be included in the improved composition to prevent infections at the wound site. The presence of the anti-oxidant, including vitamins and non-vitamin anti-oxidants, and other healing promotion materials that do not detract from, substantially interfere with, or even destroy the different thrombin activation reactions. The inventive platelet gels containing ascorbic acid retain a stable soft gel-like consistency during and after topical application at the wound site and avoid the requirement for daily reapplication.
While the inventive composition is preferably used for topical application to the exterior surface of the chronic wounds such as ulcers of the feet of diabetics, the composition may be applied to facilitate the healing of other wounds such as acute wounds such as burns. However, the composition of matter and the methods described herein are not limited solely to topical application.
The inventive composition increases the amount of growth factors in the wound, and thereby facilitates the promotion of the healing rate. This may be especially important in xe2x80x9cwoundedxe2x80x9d patients, especially those with chronic wounds who may lack sufficient circulation to facilitate the healing cascade. The invention described herein also facilitates the covering of the wound area with a substance that prevents or helps to reduce infection caused by most bacteria; and to the extent that the wound treatment material is made from autologous blood or similar biological materials, the invention described herein reduces the risks associated with the use of the treatment materials made from biological materials obtained from one or more third parties. An autologous product avoids some of the common problems associated with the use of biological materials from third parties, such as (for example) screening to assure that the donor was biologically or immunologically compatible with the patient, and otherwise free of hepatitis, HIV and the like.
In most general terms, the invention described herein expands the uses for concentrated platelet materials, especially those in gel form, by improving the speed and convenience of making the composition; the invention described herein also improves the performance of the concentrated platelet composition, by making it more useable for applications over longer periods of time, and by enhancing the wound healing and infection fighting properties. For autologous platelet gel to be more useful, the gelatinous state must be capable of remaining stable for a reasonable period of time. One aspect of the present invention is to add an anti-oxidant to the platelet gel, such as ascorbic acid.
Another aspect of the present invention involves adding one or more antibiotic substance at one or more times during the processing period so that the resulting concentrated platelet composition contains either one or a variety of the antibiotics. The use of an antibiotic in concentrated platelet compositions that enhances the complex healing cascade is indeed novel. The invention disclosed herein involves adding such substances in a manner that does not detract from, substantially interfere with, or even destroy these different reactions, pH balances and potency.
Another aspect of the present invention involves adding one or more vitamins, in addition to ascorbic acid (vitamin C) to the concentrated platelet gel. Vitamins are known to have wound healing and anti-oxidant properties. Representative examples of suitable, but none limiting, vitamins include vitamin E, vitamin A and other retinoids.
In yet another aspect of the invention, non-vitamin anti-oxidants may be included in the concentrated platelet gel. Non-limiting representative examples of such anti-oxidants include xcex2-carotene.
The method of making the invention in gel form described herein includes admixing at least one of the described additives with the plasma-poor concentrated platelets, a sufficient time before the addition of calcified thrombin (or other preferably-calcified agonist) to allow the desired dispersion of such additive(s) in such composition before gelation prevents further dispersion.